Design of miniature or small fans has to take into account of the small size of the products. A frame of the fan, after deducting the operation space required for the vanes, does not have much spared space for fastening use. Thus conventional fastening structure usually adopts the one shown in FIG. 1 in which four through holes 21 are directly formed on the four corners of the frame of the fan 20. If the installation object 10 is a power supply, the power supply has a face panel 11 which has four corresponding apertures 111. Then screws 50 are fastened by force to generate a destructive inner wall in the through holes 21 to form a fastening condition. Such an approach damages the structure of the fan 20 and affects its normal operation, notably:
1. As the fan 20 is made from plastics and formed with a thin wall due to miniaturization consideration, the forced fastening of the metal screws 50 requires the screws 50 with a larger diameter than the through holes 21. Hence the through holes 21 are slightly deformed after the screws 50 have been fastened. Due to the screws 50 are fastened to the corners with a varying depth, the stresses and deformations occurred to the fan structure also are different. As a result, the distances between the fan spindle and various corners also are different. Hence when the fan 20 rotates, air pressures at various corners also are different. This causes decreasing of heat dissipation performance. If the variation is too large, the fan 20 could generate centrifugal rotation and eccentric vibration. Asides from wearing the spindle and generating vibration, abnormal noise occurs and malfunction could happen.
2. After the fan 20 has been operated for a period of time, the vanes tend to gather dusts that must be cleared to avoid affecting operation. Then the screws 50 must be unfastened from the through holes 21. This could cause breaking of the screw or enlarging of the through holes 21. Anchoring and fastening in the succeeding re-assembly become difficult.